LeetCode 20: Valid Parentheses

Difficulty: 2

Frequency: 5

Problem:

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.

Solution:

class Solution {public:    bool isValid(string s) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        if (s.size()==0)            return true;                    if (s.size()&1!=0)            return false;                    vector<char> ParenthesStack;        for(int i = 0; i<s.size(); i++)        {            switch(s[i]){                case '(':                case '{':                case '[':                    ParenthesStack.push_back(s[i]);                    break;                case ')':                    if (ParenthesStack.size()==0||ParenthesStack.back()!='(')                        return false;                    else                        ParenthesStack.pop_back();                    break;                case '}':                    if (ParenthesStack.size()==0||ParenthesStack.back()!='{')                        return false;                    else                        ParenthesStack.pop_back();                    break;                case ']':                    if (ParenthesStack.size()==0||ParenthesStack.back()!='[')                        return false;                    else                        ParenthesStack.pop_back();                    break;                default:                    return false;            }        }                if (ParenthesStack.size()!=0)            return false;                return true;    }};

Note:

Use a stack.